1. Field of the Invention
The present invention relates to a fluorine-containing alkylsuccinic acid diester which is useful as a lubricant for a precision instrument or part with which highly precise lubrication is required, a surfactant, a mold release agent, or a rust preventive, a process for preparing said diester and a magnetic recording medium which has a lubricating layer comprising said diester.
2. Description of the Related Art
With miniaturization and tendency for high accuracy of a machine or apparatus or a part, a lubricating type of a sliding part thereof has been shifted from fluid lubrication to boundary lubrication. In particular, with electronic equipments or parts such as a VTR, a magnetic disc and the like, a ferromagnetic metal thin film is used for the increase of a recording density. Then, highly accurate lubrication is required for sliding contact of a magnetic tape or disc against a magnetic head. For example, in the case of a metal deposition tape or hard disc, a lubricant layer is formed on a magnetic layer in a thickness of only several ten .ANG. to reduce a spacing loss between the magnetic recording medium and the magnetic head as much as possible and to achieve a large output, while maintaining durability and reliability of the tape or disc. To this end, it is highly desired to develop an organic compound having good lubricity as a material for forming such lubricant layer.
As a lubricant for a metal thin film type magnetic recording medium, a fluoroalkylether group-containing monocarboxylic acid of the formula: EQU R.sub.4 COOH (1)
wherein R.sub.4 is a fluoroalkylether group has been proposed since it has good compatibility with the metal thin film (see Japanese Patent Kokai Publication Nos. 41438/1983, 127230/1984 and 58414/1987).
Recently, a perfluoropolyether ester of a monocarboxylic acid of the formula: EQU R.sub.5 --(OOCR.sub.6).sub.n ( 2)
wherein R.sub.5 is a perfluoroalkylpolyether group, R.sub.6 is an aliphatic alkyl group and n is a number of 1 to 6 has been proposed as a lubricant (see Japanese Patent Kokai Publication No. 49218/1990).
However, the lubricant comprising the fluoroalkylether group-containing monocarboxylic acid (1) or the perfluoropolyether ester of monocarboxylic acid (2) will lose its lubricity in a high humidity atmosphere.